SANFORD — Seminole County School Superintendent Robert Hughes is seeking new science buildings for Lake Howell and Lake Brantley high schools that would cost taxpayers with median-priced homes an additional $14 in taxes next year.

If the school board rejects Hughes' proposal, the same taxpayer may pay $2.50 less than this year.

Hughes suggested levying .312 mills to generate more than $1.6 million for science facilities at the two schools during last week's school board meeting. The money would be in addition to $11 million already earmarked for those projects from a $105 million bond issue passed last year.

A mill is $1 of tax for every $1,000 of taxable property value.

The additions at the two high schools originally were planned as additional rooms and labs to existing buildings, said school board spokeswoman Karen Coleman. But the school administration wants to take advantage of today's lower interest rates and build separate science buildings.

Hughes' proposal would put the school system's levy for capital outlay at 1.5 mills, the legal limit and the same as this year. The state, however, is expected to require more local contribution to school expenses, which, coupled with the science buildings, would mean a slight net tax increase.

Hughes' proposal would cost the owner of a median-priced Seminole County home about $14 more in taxes. A median-priced home has an assessed value of $80,000. With a $25,000 homestead exemption, the homeowner paid $408.76 in property taxes to the school board this year, when the millage was set at 7.432.

Under Hughes' proposal, which calls for a 7.699 millage, the same homeowner would pay $423.44, assuming the home's taxable value remained the same.

If the school board decides against Hughes' proposal, the millage would be reduced and the owner would pay $406.28 in school taxes -- about $2.50 less than this year.

As an alternative to the tax increase, Hughes proposed funding the projects with the State Science Facilities Grant of $446,000 that last year had been used for Oviedo High School's remodeling. He also said the board could dip into the bond reserve fund.

Hughes presented his proposal to board members along with a tentative $253 million budget for 1986-87. Board members will discuss the proposals at a 1:30 p.m. Wednesday workshop.

Hughes also plans this week to present a more accurate budget proposal. School administrators still expect the state education commissioner to certify the local minimum tax the school board can levy to qualify for state money. Also, a discrepancy was detected between tax roll figures used by the state Department of Education and the county property appraiser.

Another budget workshop is scheduled for 1 p.m. July 21 after which school board members must adopt a tentative budget. A public hearing is scheduled for 7 p.m. July 28.